Stirred tank impellers speed

Blend time tb, the time required to achieve a specified maximum standard deviation of concentration after injection of a tracer into a stirred tank, is made dimensionless by multipfying by the impeller rotational speed ... 

Consider a stirred tank vessel having a Newtonian liquid of density p and viseosity p, is agitated by an impeller of diameter D, rotating at a rotational speed N. Let the tank diameter be D, the impeller width W, and the liquid depth H. The power P required for agitation of a single-phase liquid ean be expressed as ... 

Figure 15.5 Measured and simulated turbulent kinetic energies (normalized with the impeller tip speed) at the impeller plane in a stirred tank reactor (From [17]).

For conventional stirred tank processing of the nitration of benzene, the dependence of conversion on impeller speed is given in [102]. 

It is worth remembering that the power requirement of gas-sparged stirred tanks per unit liquid volume at a given superficial gas velocity Uq is proportional to L where N is the rotational speed of the impeller (T ) and L is the tank size (L), such as the diameter. Usually, k a values vary in proportion to (Pq/V) " and Uq", where m = 0.4-0.7 and = 0.2-0.8, depending on operating conditions. 

One of the functions of the impeller in an aerated stirred tank is to disperse gas into the hquid as bubbles. For a given stirrer speed there is a maximum gas flow rate, above which the gas is poorly dispersed. Likewise, for a given gas flow rate there is a minimum stirrer speed, below which the stirrer cannot disperse gas. 

An aerated stirred-tank fermenter equipped with a standard Rushton turbine of the following dimensions contains a liquid with density p = 1010kgm and viscosity n = 9.8 X 10 Pa s. The tank diameter D is 0.90 m, liquid depth Hl = 0.90 m, impeller diameter d = 0.30 m. The oxygen diffusivity in the liquid Dl is 2.10 X 10 5 cm- s T Estimate the stirrer power required and the volumetric mass transfer coefficient of oxygen (use Equation 7.36b), when air is supplied from the tank bottom at a rate of 0.60 m min at a rotational stirrer speed of 120 rpm, that is 2.0 s T... 

For an animal cell culture, satisfactory results were obtained with a pilot fermentor, 0.3 m in diameter, with a liquid height of 0.3 m (clear liquid), at a rotational impeller speed N of 1.0 s (impeller diameter 0.1 m) and an air rate (30 °C) of 0.02 m min. The density and viscosity of the broth are 1020kg rn and 0.002 Pa s, respectively. The value can be correlated by Equation 7.36b. When k a is used as the scale-up criterion, and the allowable impeller tip speed is 0.5 m s , estimate the maximum diameter of a geometrically similar stirred tank. 

S3] A process for the oligomerization of ethylene for the production of linear a-olefins had to be developed in stirred tank reactor assuming isothermal conditions and was executed in the kinetic regime. The latter was assured by increasing the rotational speed of the impeller until the rate of reaction did not increase further. The autoclave reactor was heated by an external blanket and supplied with cooling water circulation through an internal coil. 

When stirred-tank bioreactors started to be used for animal cell cultivation, many problems related to deleterious effects of agitation on cell viability were observed. Flowever, it was noted that the use of large impellers rotating at low speeds could minimize mechanical damage to the cells. The most widely used impeller types are marine (Chisti, 1993)... 

The stirred-tank bioreactor is an example of a reactor that is scaled-up by direct increase of its volume. One of the critical parameters that should be evaluated at different scales is the rotation speed of the impeller. Different criteria can be employed ... 

During the mixing of a single-phase liquid in a stirred tank, the important parameters are the rate of power input, P, the impeller stirring speed, N, gravitational acceleration, g, the fluid density, p and viscosity, p, the impeller diameter, D and the other geometric characteristic lengths of the vessel (i.e. baffle width and depth, impeller shape,... 

Armenante, P.M. Uehara Nagamine, E. Effect of low off-bottom impeller clearance on the minimum agitation speed for complete suspension of solids in stirred tanks. Chem. Eng. Sci. 1998, 53, 1757-1775. 

The critical mixing factors in a stirred tank at e impeller speed and type, as well as their influence on local turbulence and overall circulation. Since all aspects of these factors cannot be maintained constant on scale-up either locally or globally, the extent to which changes in the crystallizing environment will affect nucleation is extremely difficult to predict. To the mixing issue must be added the uncertainties caused by soluble and insoluble impurities that may be present in sufficiently different concentrations from batch to batch to cause variation in induction time, nucleation rate, and particle size. 

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